With the number of Americans who take more than one drug for their well-being increasing, there is an increasing risk of adverse events due to drug-drug interactions. New tools are necessary to understand biology at the initiation of the drug metabolic process, i.e., transcriptional regulation. Since multiple enzymes may act on a given drug, and multiple transcription factors may activate an enzyme, the problem becomes quite complex. In addition, new in vitro tissue engineered models that recapitulate the human physiology are required to get an accurate approximation for the in vivo response of drugs. We propose to extend out microphysiological in vitro liver model to a liver-on-a-chip array to study in high-throughput the transcriptional activity of enzymes and apply it to the study of drug-drug interactions (DDIs). Our tissue engineered construct will use both primary human cells and induced pluripotent stem cells (iPSC)-derived cells. This project will be carried out by distinct research groups. The PIs have a very strong collaborative record of accomplishment. Dr. Martin Yarmush (MGH) will oversee tissue engineering of the liver-on-a-chip and the drug interaction studies. Dr. Mehmet Toner, Director of the BioMEMs Resource Center at MGH, will lead the microfabrication group focusing on the development of microfabricated array. The iPSC-derived cells will be sourced from Dr. Yoon Y Jang at Johns Hopkins University.